Diesel engines run better once they're warmed up - in fact, larger ones like my Powerstroke, run like total S*** until they've been up to 160F+ for a few minutes (it's true they don't get there just idling, as you mentioned). Even the best synthetic oils don't lubricate well at sub-zero temps, increasing the wear in sensitive and hard-to-lube areas like cylinder walls. Metals expand and contract as they're heated and cooled, and the more rapid the heat change the weaker the metal becomes. On cold days, some parts of our cars will go from -40F to over 1200F over the course of a drive and the slower that change occurs, the stronger those metals will remain.
I know that idling the car for 3-4 minutes won't warm it completely up to operating temp, but it's definitely better long-term for the car than hopping in at -20 or -30F, starting it up and putting it right in gear (not to mention, the ice and snow on the windshield that I can't always scrape off). And the manufacturer's know this, but they also know that related problems don't sneak up until after the warranty is gone; the reason they say not to idle or do long warm-ups, aside from the DPF, is because it hurts the driver's perceived fuel mileage. I have a block heater, and I don't know how extensive this setup is but I'll likely end up with a oil pan heater, and a trans pan heater, by this next winter if there isn't already one there.
I've been thinking more about the DPF thing as well, and driving a cold engine is gonna fill that thing up with soot pretty fast, and I wonder if it equals out to being similar to the amount of soot built up during a 10-minute idle and hitting the same stretch of road with a now-warm-and-efficient engine.
One of the worst things for any engine is driving it like normal when it's cold, metal becomes very brittle at the temps we see here in the winter and suddenly adding heat to it will cause it to rapidly expand, which weakens the metal more than a gradual warm up. Here's one last food for thought - there's a lot of guys on here and other forums that talk about properly cooling down your turbo before shutting down your engine (due to the rapid heat change by shutting down a hot turbo). Why would warming the turbo up be any different?
MN gets cold, too! You guys get colder than us sometimes lol! I sure hate getting into a car at in the cold, I've actually frost nipped fingers doing it on a few occasions. Burrrrr!
I'll be getting a remote start on my car, is there anyone out there that has one?
Cheers!
~Joe